| // This file was extracted from the TCG Published |
| // Trusted Platform Module Library |
| // Part 4: Supporting Routines |
| // Family "2.0" |
| // Level 00 Revision 01.16 |
| // October 30, 2014 |
| |
| #include <stdlib.h> |
| #include <stdint.h> |
| #include <memory.h> |
| #include "TpmBuildSwitches.h" |
| // |
| // |
| // Local values |
| // |
| // This is the last 32-bits of hardware entropy produced. We have to check to see that two consecutive 32- |
| // bit values are not the same because (according to FIPS 140-2, annex C |
| // “If each call to a RNG produces blocks of n bits (where n > 15), the first n-bit block generated after |
| // power-up, initialization, or reset shall not be used, but shall be saved for comparison with the next n- |
| // bit block to be generated. Each subsequent generation of an n-bit block shall be compared with the |
| // previously generated block. The test shall fail if any two compared n-bit blocks are equal.” |
| // |
| extern uint32_t lastEntropy; |
| extern int firstValue; |
| // |
| // |
| // _plat__GetEntropy() |
| // |
| // This function is used to get available hardware entropy. In a hardware implementation of this function, |
| // there would be no call to the system to get entropy. If the caller does not ask for any entropy, then this is |
| // a startup indication and firstValue should be reset. |
| // |
| // Return Value Meaning |
| // |
| // <0 hardware failure of the entropy generator, this is sticky |
| // >= 0 the returned amount of entropy (bytes) |
| // |
| LIB_EXPORT int32_t |
| _plat__GetEntropy( |
| unsigned char *entropy, // output buffer |
| uint32_t amount // amount requested |
| ) |
| { |
| uint32_t rndNum; |
| |
| if(amount == 0) |
| { |
| firstValue = 1; |
| return 0; |
| } |
| // Only provide entropy 32 bits at a time to test the ability |
| // of the caller to deal with partial results. |
| rndNum = random(); //TODO(vbendeb): compare to rand_s case |
| if(firstValue) |
| firstValue = 0; |
| |
| lastEntropy = rndNum; |
| if(amount > sizeof(rndNum)) |
| amount = sizeof(rndNum); |
| memcpy(entropy, &rndNum, amount); |
| |
| return (int32_t)amount; |
| } |